1. The Field of the Invention
The present invention is related to an ignition system for use with a flare warhead. More particularly, the present invention is related to an insensitive flare ignition system utilizing a combustible train to carry an explosive shock from the ignition initiator to the illuminant igniter.
2. Technical Background
Flares of various types have found useful application to accomplish a variety of purposes. For military purposes, for example, it is often desirable to light a particular area at night. A flare may be used to produce light for search and rescue operations, or for various other military purposes. When used in these applications, flares are typically mounted to a rocket motor and launched to a predetermined target area. A parachute is generally mounted to the flare and designed to deploy over the target area, thereby permitting the flare to slowly descend while emitting light.
Typical of prior-art flares is the M-257 Standoff Illuminating Flare, made for the U.S. Army, and designated generally at 10 in FIGS. 1 through 4. As illustrated in FIG. 1, the end of the flare 10 includes a motor adapter 12 upon which a rocket motor may be threadably attached. The flare 10 further includes a fuse 14, a drogue parachute 16, a main parachute 18, flare illuminant 20 and an illuminant ignition system 22.
Fuse 14, housed within the motor adapter 12, is armed upon initial acceleration of the rocket motor. The M-257 employs what is commonly referred to as a "setback fuse" which includes a slider 24 which is of sufficient mass that it compresses a spring 26 upon initial acceleration of the rocket motor. Rocket motors commonly employed in propelling such flares generally have an initial acceleration of about 60 g-forces (approximately 770 m/s.sup.2) over a period of about one second.
Upon burn-out of the rocket motor, the slider 24 is forced back to the position illustrated in FIG. 1 by the extension force of the spring 26. Upon reaching the end of its travel, the slider 24 releases a firing pin which fires a primer cap (not shown). The primer cap is positioned contiguous a pyrotechnic delay column (not shown) such that firing of the primer cap ignites the delay column. The delay column burns for a predetermined period of time, generally about nine seconds, while the flare is coasting through the air. While coasting, the flare slows from its maximum velocity of about 2200 ft/sec to about 750 ft/sec.
At the base of the delay column is positioned a propellant wafer 28 which acts as the first separation charge. Upon burnout of the delay column, the separation charge is ignited. The firing of the separation charge results in the buildup of a pressure of approximately 5,000 psi. Upon ignition of the pro pellant wafer 28, a pusher plate 32 bears against the aft end of the drogue parachute housing 34, thereby tending to separate the warhead from the rocket motor. The force of separation resulting from the internal pressure buildup causes shear pins 30 which attach the motor adapter 12 to the remainder of the flare to shear. Upon the shearing of shear pins 30, the motor adapter 12 and rocket motor are released from the warhead, as illustrated in FIG. 2.
Upon separation, the pusher plate 32 falls away from the main parachute housing and becomes subject to the substantial resistance forces imposed by the atmosphere. The pusher plate 32 is attached to the drogue chute 16. Hence, the force of air resistance on the pusher plate 32 pulls the drogue chute 16 out of the housing 34 and permits it to inflate.
At the same time, a deflector plate 36, attached to the motor adapter 12, falls off to the side of the motor adapter 12. The force of air resistance acting on the deflector plate 36 causes the deflector plate 36 to function as a drogue and alter the trajectory of the combined motor adapter 12 and the rocket motor, thereby assisting to prevent the possible collision of the rocket motor with the flare.
With continued reference to FIG. 2, a gas generator 38, mounted within the parachute housing 34, is ignited upon deployment of the drogue parachute 16. A nylon cord or wire 40 connects the bridle 42 of the drogue parachute 16 to a "quick match" 44 located inside the gas generator 38. The cord or wire 40 is shorter than the main drogue line 46; thus, as the drogue parachute deploys, the quick match 44 is pulled out of the gas generator 38 and ignition of the generator is effected.
The gas generator 38 acts as a delay to control how long the drogue parachute is deployed. In the M-257 standard flare, the gas generator 38 provides an approximate two-second delay. The head end of the gas generator 38 is positioned contiguous a propellant wafer 48 which functions as a secondary separation charge. Thus, as the gas generator 38 burns out, it ignites the propellant wafer 48.
In the M-257, the secondary separation charge generates an internal pressure of about 10,000 psi. This pressure causes a second pusher plate 50 to bear against the aft end of the main parachute housing 52 and results in the shearing of shear pins 54 which attach the drogue chute housing 34 to the main chute housing 52. As the shear pins 54 are broken, the drogue chute 16 and the drogue chute housing 34 are separated from the remainder of the flare, as illustrated in FIG. 3.
The second pusher plate 50 then falls out and is exposed at high speed to the atmosphere. The resulting force of air resistance on the second pusher plate 50 deploys a pilot parachute 56 to which the second pusher plate 50 is attached.
The pilot parachute 56 is connected to a main parachute container 58 in which the main parachute 18 is housed. The force on the main parachute container 58 resulting from the deployment of the pilot parachute 56 causes the main parachute container 58 to be extracted from the main parachute housing 52. As the line 60 connecting the pilot chute 56 to the main parachute housing 52 and the main parachute line 62 are fully extended, the force of the resulting jerk is sufficient to break the cotton ties 64 which hold the main chute 18 within the main chute container 58. As the cotton ties 64 break, the main parachute is deployed, as illustrated in FIG. 4. With the main parachute 18 deployed, the flare descends at a rate of approximately 13 ft/Sec.
The flare ignition system 22, as illustrated in FIG. 1, is armed upon initial acceleration of the flare. The forces due to the acceleration of the flare cause a "zig zag" safety block 70 to compress a spring 72. The safety block 70 and spring 72 are concentrically mounted about a mounting column. The safety block 70 includes a pawl which rides in a zig-zag shaped track located within the mounting column. In order for the safety block to follow the track and completely compress the spring, the flare must have an acceleration of 60 g-forces over a period of about one second.
Once armed, the flare is ignited by pulling an ignition lanyard 74. The ignition lanyard is attached at one end to the main chute line 62 and at the other end to the ignition system 22. The ignition lanyard passes from the main chute line to the ignition system along a raceway between the illuminant 20 and the canister. Within the ignition system 22, the lanyard is attached to a slider 78.
Upon deployment of the main parachute 18 (FIG. 3), the ignition lanyard 74 is pulled, causing the slider 78 to move across its track. A hammer (not shown) is retracted against a spring as the slider 78 is pulled across its track. As the slider 78 reaches the end of its track, the hammer is released and, under the force of the spring, strikes a priming cap which fires into a pellet basket 80 containing a number of BKNO.sub.3 pellets.
As best viewed in FIG. 1, a layer of foam 82 serves to tightly pack the pellets as a guard against vibration of the pellets. As the pellets burn, the heat from the pellets ignites the propellant wafer 84. Ignition of the pellets and wafer 84 generates sufficient heat to ignite the flare illuminant 20 at the head end of the flare. Additionally, the internal gas pressure generated upon ignition of the wafer 84 blows the ignition system 22 off of the flare (FIG. 4), leaving the flare open to the atmosphere and permitting the approximate 1 million candle power of light generated by the flare to shine out of the flare canister and onto the area to be illuminated.
The M-257 was originally designed to work with a fixed-delay fuse. The standard fixed-delay fuse utilized in the M-257 provides a constant delay of 13.5 seconds from launch to flare ignition. This corresponds to a fixed standoff range of about 4,200 meters from launcher to target and a parachute deployment velocity of 250 m/sec.
In recent years, however, the demand for a variable range flare has resulted in the development of variable delay fuses. The range of the flare is thus controlled by utilizing a fuse which can vary the time between when the rocket motor fires and when the drogue parachute deploys.
A significant disadvantage to the ignition system 22 of the M-257 is that it is not reliable over a wide range of parachute deployment velocities. At particularly low velocities, the force on the ignition lanyard resulting from the deployment of the main parachute is insufficient to trigger the firing of the ignition system. Additionally, at high velocities, the extreme jerk on the ignition lanyard frequently results in the lanyard being broken without pulling the slider and triggering ignition of the ignition system.
The M-257 ignition system incorporates a variety of parts, such as the safety block 70, the slider 78 and the hammer and priming cap mechanism which ignites the pellet basket 80. All of these parts add to the complexity of the manufacture of the ignition system. Incorporating so many mechanisms which must all function together properly in order for the flare to be ignited presents an increased probability of malfunction over more simple designs.
Thus, it would be an advancement in the art to provide an improved ignition system for a flare warhead which would function effectively regardless of flare velocity at the time the ignition system is triggered.
Indeed, it would be an advancement in the art to provide such an ignition system which reduced the number of moving parts thereby enabling the ignition system to be simpler to manufacture and more reliable than prior-art ignition systems.
Such an improved flare ignition system is disclosed and claimed herein.